AFT-58 (SOLTI-2101): A Phase III, Multicenter, Open-Label Study of Ribociclib vs. Palbociclib in Patients with Advanced Hormone Receptor-Positive/HER2-negative/HER2-Enriched Breast Cancer, Harmonia TrialAFT-58 (SOLTI-2101): A Phase III, Multicenter, Open-

AFT-58 (SOLTI-2101): A Phase III, Multicenter, Open-Label Study of Ribociclib vs. Palbociclib in Patients with Advanced Hormone Receptor-Positive/HER2-negative/HER2-Enriched Breast Cancer, Harmonia Trial Primary: 1. To compare PFS of ribociclib plus endocrine therapy over palbociclib plus endocrine therapy with respect to PFS in patients with advanced hormone receptor-positive, HER2-negative and HER2-E breast cancer. Secondary: 1. To compare the two treatment arms with respect to PFS2 in the HER2-E cohort 2. To compare the two treatment arms with respect to overall survival in the HER2-E cohort 3. To evaluate the two treatment arms with respect to ORR and clinical benefit rate (CBR) in HER2-E patients, where CBR, defined as percentage of patients with CR, PR per RECIST 1.1 or SD lasting 24 weeks or longer. 4. To describe time to response and duration of response in each treatment arm. 5. To evaluate the safety and tolerability of ribociclib and palbociclib in combination with endocrine therapy the HER2- E cohort 6. To evaluate patient reported outcomes for health-related quality of life in the two treatment arms of the HER2-E cohort.